Well,
Ive been a camp counselor for a large scout camp way back!
I think you need to tell your boss about it aasap! These days they'd be hard pressed to then change or not hav you do this as that could be construed as an illegal act on several counts...they cant hold a disability (which is the classification I don't use but it is) against you unless is compromises your ability to do your job.
Now on to what you wear for protection.
If your limited to changes you'll need a good quality and thick diaper...say 24/7's
They will most likely show a bit, if someone knows what to look for, but wear a onesie over it, and it will not show much and most people will just think you wear an undershirt...
But, based on the camps I've been at, there are plenty of facilities that you can use...
As a camp counselor i always carried a backpack with lots of things in it, from first I'd kit, to medications...back then all the counselor handeled meds for the kids...
So, you may have a pack with you too, there are emergencies that you need to be prepared for, I'm sure you'll need a first aid kit, epi pens, topical creams for poison ivy/etc and keys plus books and guides for activities.
So, you should have enevrthing you need with, including your diapers too.
Talk to your boss...he can filll you in on what you'll need with, but even if they done require anything, I'd still bring a pack with first aid, Epi, sunblock, aloe, etc...better to have it and not no it, as to needing it and not having it...
Boy Scout motto, be prepared!